Ye' old general discussion board. Basically, for everything that isn't covered elsewhere. Come here to shoot the breeze, shoot your mouth off, or whatever suits your fancy. This forum is not for asking programming related questions.
I love the one you mentioned. Works great. You can completely customize the output (comes with support for a number of template systems, as well as the ability to write your own renderer plugin)... write plugins for extra rules/filtering. It's great. Form validation is so easy now that I use it.
Maybe have a look at Manuel Lamos' class Forms generation and validation at phpclasses. Haven't used it myself but have been keeping an eye on it. Looks very complete and is in very active development. Is at ranking no 1 on phpclasses so it's certainly not the worst class there.
Another one which I do have experience with is http://www.formhandler.net/. Works very well and is quite complete too. It's a class which let you generate forms easily and do stuff with the results (show error messages, email data or sent th data to db, etc). However, as it is a standalone complete class, I'm not sure how easy it will be if you have special needs or want to integrate it (functionally) in an existing framework of code. You'll have to take a look at the code for that.
Sorry I can't give you more details, but maybe these 2 are interesting enough to have a look at.
Yes I guess that's a drawback of many existing solutions: it's hard to control the exact output. In other words, you'll get a bunch of tables, no css, no clean markup etc. (if you find one, please let me/us know)
I can't be bothered to even look, as I'm not a huge fan of FORM generators, but I've suggested to Oren he considered looking into writting a CSS generator...
like I said... HTML_QuickForm lets you customize the output. I haven't done it yet, because so far it's been very easy to just style the generated forms (but I haven't used it for any real complicated forms yet). It allows you to write your own renderer and has built-in support for smarty and a couple other template engines. I was considering writing my own until I found this one. Very easy and fast.
Also, for those of you who aren't aware, this is a Pear package.